1. Field of the Invention
This invention is generally directed to a process of applying corrosion resistant coatings to products manufactured of sheet metal and more particularly to such a process wherein coil coating techniques are utilized to provide corrosion resistance to selected areas of a coil of sheet metal through the application of one or more stripes of corrosion resistant coating(s) along the upper and lower surface of the metal. The process of the present invention provides for the selective application of corrosion resistant coatings to sheet metal products prior to their being cut, stamped, bent or otherwise formed from a coil of sheet metal so that only those surfaces of the product being formed which require corrosion protection are coated thereby substantially conserving resources in the manufacturing process and decreasing cost of product manufacture.
In a preferred embodiment, coils of galvanized sheet metal are selectively coated with corrosion resistant material along portions of their upper and lower surfaces after which the metal is cut and formed into sheet metal nails of the type disclosed in applicant's copending application Ser. No. 07/701,843 so that only the heads of the fasteners are coated leaving the galvanized material on the legs or shanks uncoated for purposes of promoting chemical bonding between the nails and cementitious materials into which such fasteners are driven.
2. History of the Related Art
Heretofore, products manufactured from sheet metal which had to be treated to provide corrosion resistance were either preformed and then dipped in a bath of corrosion resistant material or sprayed to apply a corrosion resistant coating. The first such process required large vats of corrosion resistant chemicals to be maintained into which products could be dipped after which the products were removed and allowed to dry. The drawbacks of such a process include the exposure of large quantities of potentially harmful chemicals to the atmosphere thereby creating a potentially hazardous and unsafe work environment. In addition, coatings often drip from parts or products after being dipped thereby creating a waste control problem and further contributing to work-place contamination. Also, such coating processes create an immense waste of expensive corrosion resistant coating materials by applying the coatings to an entire product in instances where only portions of the product require corrosion protection.
In spraying applications, the same environmental contamination and hazardous work-place conditions are created. Particles of corrosion resistant coatings are released into the atmosphere requiring complex exhaust systems to remove caustic and toxic chemicals from the air to protect workers' health. Such systems require expensive filters to remove the chemicals so that damage to the surrounding environment by the release of such chemicals into the atmosphere is effectively prevented. Although this type of coating allows a more selective application of the coating material to a product, there remains a large quantity of waste which is sprayed on portions of the product which do not require the coating and a large amount of spray which also does not contact the product and thus must be recovered or cleaned from work areas.
In order to overcome many of the drawbacks of dip and spray coating techniques in the painting industry, a technology was developed for priming and coating sheet metals prior to their being cut, shaped or otherwise formed into an end product. The process involved is known in the industry as "coil coating" which is a method of cleaning, treating, priming, painting and finishing sheet metal prior to its being processed into an end product thereby eliminating the need for in-plant coating lines in manufacturing facilities. In a conventional coil coating process a coil of raw sheet metal is unwound and thereafter cleaned and rinsed as it is continuously drawn towards a coating area. Conventionally, the sheet metal is chemically pretreated after being cleaned and rinsed in order to prepare the surface for accepting a coating such as a primer or paint. Such coil coating processes may be utilized to apply selective coatings of different materials to both the upper and lower surface of the sheet metal in a continuous process. After the sheet metal has been coated, it is passed through ovens where the coatings are cured. The sheet metal is thereafter recoiled for shipment to end users. In some instances, the material, following its coating, may be cut or slit into sheets or smaller coils depending upon the exact end use of the sheet metal.
Although coil coating has been utilized in the industry to provide primer or finish paint coats on sheet metals such techniques have not been utilized to provide predetermined and localized corrosion protection to materials which will thereafter be cut and shaped to form end products such as flat metal fasteners utilized in the roofing industry. Generally, coil coating techniques provide for coating the entire upper and lower surfaces of metal and not predetermined or selected areas of the metal during the coating process.